The present invention relates generally to cutoff valves, and more particularly to a fluid cuttoff valve for use in fluid systems in which flow is controlled between a source of high pressure and an environment at a reduced pressure such that excess flow rates and excess pressures are not experienced in the environment.
Fluid systems having a fluid supply source and an environment in which the fluid is subjected to a controlled use are old and well known. In some applications the source is at a relatively high pressure, e.g. 3,000 psig and the environment is at a relatively low pressure, e.g. 5 psig, and thus a fluid system necessarily requires a flow control mechanism and/or a pressure reducing station. Such a station might comprise a pressure regulator which ensures that the environment experiences the desired pressure. However, an additional device is usually necessary to protect that portion of the system downstream of the pressure reducing station from excess pressure in the event that the station malfunctions or excess flow in the event of a loss of system integrity, e.g., a pipe or hose bursting between the fluid supply source and the environment.
Devices to protect against excess pressure have traditionally taken the form of relief or safety valves, rupture discs or electrical trip cutout valves. Excess flow rate protection has been accomplished by conventional devices commonly referred to as flow fuzes or pneumatic fuzes. This latter device is exemplified by U.S. Pat. No. 3,621,873, issued to Kenann et al, issued Nov. 23, 1971.
Certain fluid systems require simultaneous protection against the possibility of an excess pressure condition, which results possibly from the malfunction of the regulating or control device, and an excess flow rate condition which is symptomatic of a structural failure in the fluid system boundary. This is particularly true in the fluid systems of submersibles or marine research vessels which handle highly combustible life support fluids such as oxygen and wherein some of the usual methods for disposal or containment of excess fluids are not available. For example, in an oxygen bleed system on a submersible because of the limited and strictly confined environment, there is no feasible alternative for absorbing any excess fluid. Also, discharge outside of the hull of the submersible is usually impractical due to the possibility of detection by unfriendly sensors and because the ambient pressure surrounding the submersible is generally much higher than that within the environment of the submersible.
For these reasons, no relief protection is provided for the above mentioned system and presently malfunctions such as a jammed regulator poppet or a torn sensing diaphragm can result in an overpressure condition producing material damage and injury to personnel. Further, because oxygen is being used, an untoward combustion hazard exists. If there is a fire anywhere in the fluid system, e.g., in the regulator, possibly caused by high velocity throttle impingement, or at some other location downstream in the fluid system, the regulator will open fully because it senses a flow demand. The full opening of the regulator will feed the combustion process by dumping out the entire capacity of the oxygen storage tanks into an area of the submersible where the combustion is occurring. It is clear that the potential for seriously jeopardizing the survival of a submersible is greater by not providing a fluid protection device. A current solution to this problem has been the installation of flow limiting orifice in front of the regulating valve. Unfortunately this is an entirely futile approach because of the range over which the source pressure can vary, e.g., 60 to 3000 psig.
A requirement thus exists for a single fluid cutoff valve which can quickly and reliably respond simultaneously to either an excess pressure or excess flow rate condition in order to isolate a fluid supply from an environment in which the fluid is used.